In an electrical energy usage contract executed between an electric power company and an electric power consumer, electric charges are divided into basic charges, which are fixed-rate portions, and fluctuating-rate portions, which are determined based on consumed electrical energy. The total of both portions described above is computed as electricity charges, and is borne by consumers. The basic method for establishment of the basic charges, which are the fixed-rate portions as stated above, is described as follows. That is to say, electric power companies integrate electrical energy continuously consumed by electric power consumers during multiple given time segments (e.g., 30 minutes each). The electrical energy obtained as a result of the aforementioned integration is measured as a demand value for the relevant time segments. The monetary amount that matches the predetermined reference value corresponding to the largest demand value (i.e., maximum demand value) among demand values measured as above within a previous predetermined period (e.g., 1 year) is used as a basic charge for the subsequent prescribed period.
The aforementioned system will be explained in detail with reference to FIG. 1. FIG. 1 is a bar graph indicating changes in monthly demand values of electric power consumers. The term “monthly demand value” refers to the maximum demand value within a corresponding month. The vertical axis of FIG. 1 represents electrical energy demand value. The predetermined period stated above is set to be one year from July 1 of each year through the last day of June of the following year. The monthly basic charge for the year from July 2010 through June 2011 is assumed to have been 2,800 yen.
As shown in FIG. 1, as a result of a sharp increase in electrical energy usage in June 2011, 3,200 yen, which was the basic charge for the coming year, was exceeded by the corresponding electric power consumer. In this case, 3,200 yen was used as the yearly basic charge starting July. That is to say, the basic charge increased by 400 yen, which was approximately a 14% increase over the previous charge. No matter how far the demand value fell, 3,200 yen remained the basic charge. Additionally, in the case of major electric power consumers, if demand values exceed the electrical energy values determined upon execution of contracts, penalties, such as penalty charges corresponding to such excesses, may be imposed on such consumers.
As described above, in case that a demand value increases even temporarily, even if such demand value subsequently falls, the basic charge will be fixed at a high level. Therefore, electricity consumption activities (i.e., energy-saving actions) that allow lower demand values serve the medium- and long-term economic interests of individual electric power consumers. Therefore, conventionally, technologies that allow the extent to which demand value has changed to be displayed based on a relationship with the reference value upon determining basic charges for electric power companies for a predetermined time segment and allow easy understanding of such changes have been demanded.
In this regard, in Japanese Examined Patent Application Publication No. No. 4775749, an example of the technology used for a demand target display device is disclosed. This device sets up predetermined reference values for computation of basic electric charges as upper limit targets (i.e., target demand values), and displays the relationships between such target demand values and demand values at predetermined times using a disc-shaped clock outer edge.